Bogies are respectively mounted under a floor of a car body of a railway vehicle such as a light rail vehicle and drive along rails while supporting the car body. A general bogie has a construction in which a pair of axles are rotatably attached to front and rear sides of a bogie frame and a pair of wheels are mounted to each axle. Various devices such as air springs for absorbing a vibration of the car body and a motor for rotating the axles are mounted to the bogie frame.
In the vehicle including the bogies described above, since the car body on which passengers get is provided on the bogies, the floor surface of the car body is provided at a position that is distant from the ground, thereby generating a difference in height between an entrance of the car body and the ground. Accordingly, in recent years, to achieve barrier-free purposes, a low-floor railway vehicle appears, which is provided with an entrance at a lower position to enable elderly persons, handicapped persons, and others to easily get on and out of the car body.
For example, in a bogie disclosed in EP Patent Publication No. 348378, an axle for coupling right and left wheels is omitted, and wheels are directly rotatably attached to a bogie frame. In addition, one of two pairs of wheels have a larger diameter and the remaining pair of wheels have a smaller diameter. In this construction, the floor surface of the car body which is located above the small-diameter wheels can be made lower, and there can be formed a space in which components and members are disposed between the large-diameter wheels.